WASHINGTON – Former city top cop Bernard Kerik, moments after President Bush nominated him yesterday to run the Homeland Security Department, said his firsthand experience on 9/11 has taught him the importance of his new post.

“I know what is at stake. On September 11, 2001, I witnessed firsthand the very worst of humanity,” Kerik said during the White House ceremony for his nomination.

“I promise you, Mr. President, that both the memory of those courageous souls and the horrors I saw inflicted upon our proud nation will serve as permanent reminders of the awesome responsibility you place in my charge.

“I pledge to work tirelessly to honor them, and your trust in me.”

Bush called the bald-headed, barrel-chested Kerik an “accomplished and effective leader,” and also invoked the Sept. 11 attacks.

“Bernie Kerik understands the duties that came to America on September the 11th,” said Bush, standing in the formal Roosevelt Room in the White House.

“The resolve he felt that morning will guide him every day on his job. And every first responder defending our homeland will have a faithful ally in Bernie Kerik.”

Bush and Kerik both thanked former Mayor Rudy Giuliani, who has played a key role in Kerik’s meteoric career, tapping him to run the city’s Correction Department and then the NYPD.

Kerik also went to work for Giuliani’s private consulting firm after leaving the city payroll in 2002.

“When you see him, he’s a big strong guy with a black belt,” Giuliani said of Kerik’s appearance.

“What you get to know when you work with him is how smart he is … how effective and sophisticated a manager he is.”

Kerik was a strong supporter of Bush during the re-election campaign, defending the president from charges by Democratic challenger John Kerry that Bush had failed on many fronts to adequately protect the country against new attacks.

Giuliani didn’t attend the ceremony, but Kerik’s wife, Hala, and three of his children sat in the front row of chairs facing the president.

The Syrian-born Hala seemed preoccupied during most of the ceremony by her two youngest daughters, Angelina and Celine, who played with small plastic purple Easter eggs.

At one point, one of the eggs fell to the floor and rolled toward Bush’s feet.

Giuliani’s key aide, Tony Carbonetti, sat behind Kerik’s family.

Before the ceremony began, Bush political adviser Karl Rove walked across the room to chat with Carbonetti: “What’s up, dude?” Rove asked.

Kerik would take over a department only two years old, established by Congress to bring together 22 federal agencies to improve defenses against terrorism.

The department has 180,000 employees and a combined budget of $36billion.

Joe Allbaugh, the former Federal Emergency Management Agency director, who was also mentioned as a candidate for the job, said Kerik will be “drinking water from a fire hose for quite a while, but I know he’s up to the challenge.”